T3 only blood results - help much appreciated

Hi all,

I've been on T3 only (20mcg) since mid-October, which I take once a day in the morning. I had a blood test last week in the morning before I took my dose and results were as follows:

TSH - 1.6 (0.27 - 4.2)

FT4 - 0.6 (12-22)

FT3 - 2.6 (3.1-6.8)

These are quite different to the results I had three weeks after starting T3:

TSH - 0.02

FT4 - 4.4

FT3 - 3.5

Even when I was on 75mcg levo, my TSH hadn't been above 0.09 in over a year, accompanied my mid-range FT4 and low FT3.

I don't really know what to make of the new results, some of my symptoms are better (notably my sluggish digestion and brain fogginess), but other things have not improved or have got worse e.g. anxiety/heart feeling 'heavy' and issues with exercise tolerance. My body temperature never reaches 37 and has dropped as low as 35.4 on occasion (not that I monitored it on T4). I have sometimes taken an extra piece of tablet (quarter to half) if I've felt like I needed it, especially for the anxiety, but didn't for 3 days before the blood test.

Could the first test have been too soon after starting T3 to see how it was working?

I had a stomach bug a week before the second test, could this have affected the result?

Also, as the test was just over 24 hours since the last dose, would that put ft3 mid-range rather than under?

Based on the results from 3 weeks after starting, my endo wanted to switch me to 25mcg levo and 10mcg T3, but my GP allowed me to stay on 20mcg T3 to give it a couple of months. I've got an apt with my GP tomorrow, and supposed to be seeing the endo next week - I say supposed because I'm tempted to seek a second opinion. I don't quite know how to approach tomorrow's appointment.

If anyone can help me make sense of this at all it would be very much appreciated.


Emma x

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11 Replies

  • T4 has a half life of 6-7 days, so at the 3 week point, you still had some of it in your system (assuming you stopped taking it one day and started taking T3 the next?). That might be why your results looked better.

    Quite simply, you're not on enough T3 now. 20mcg is rarely a replacement dose - most people need at least twice that (with some exceptions). Your FT3 is under range, so it seems clear to me you need more. TSH is largely irrelvent on T3 only (it's usually suppressed) and FT4 will be correspondingly low because your pituitary gland won't be asking your thyroid to produce any.

  • Thank you, yes I did stop levo and start t3 the next day. I was v surprised at my tsh, fully expected it to be suppressed. Endo will be delighted...!

  • Mountaingoat, You are undermedicated. It's natural that FT4 is below range as you are taking T3 only, but FT3 is also below range. Most people on T3 only will need FT3 in the top third of range to feel well ie >5.5, and will have low, or even suppressed, TSH. I think you probably need 40mcg T3, or 20mcg T3 + 50mcg Levothyroxine.


    I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.

  • Thank you Clutter. With determining whether it's in the top part of the range, how much does the timing of the blood test affect it? Ie lots of people split their dose so a morning test might only be 12 hours after the last dose whereas it's 24 for me. Am I making any sense?!

  • Mountaingoat, as you left 24hrs between last dose and blood draw you can probably extrapolate your result by +20% ie normal circulating FT3 will be estimated at 3.12, which is bottom of the range so still very low.


    I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.

  • Thank you, that's helpful to know. I thought it might be half.

  • Can you give the ranges of your results above, please. TSH isn't so important.

    20mcg if only approx 60mcg of levo which is an extremely low dose. 25mcg T3 is around 75 to100mcg levo (equivalent).

  • Hi Shaws, ranges are in brackets by the first set of results. Thanks, Emma

  • Also, is it weird that some days, like today, I feel completely fine and others I hit the wall?

  • No, it doesn't sound weird. We need a constant dose which is high enough to give no 'ups/downs' but a constant everyday 'smooth' journey.

    If we use our energy 'that's the T3' which has to saturate our receptor cells first - then it's work begins and lasts for between 1 to 3 days. You have to ask for an increase. This is an excerpt re TSH:

    the measurement of the TSH level in the blood can no longer be quite such an accurate, sensitive or reliable indicator of the health of your thyroid as generally supposed.

    Furthermore, a TSH measurement won't tell you if:

    you are converting enough T4 into T3, or

    you are converting too much T4 into reverse T3, or

    your thyroid is being attacked by antibodies, or

    you have T3 receptor resistance, or

    you are suffering from adrenal insufficiency, or

    you are deficient in those minerals and vitamins essential for good thyroid health.


    If we don't have sufficient thyroid hormones it can cause other more serious problems.

  • Thanks Shaws, hopefully my GP will be in listening mode tomorrow, she's normally pretty good.

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